[N+:1]([C:4]1[NH:8][N:7]=[C:6]([C:9]([O:11][CH3:12])=[O:10])[CH:5]=1)([O-:3])=[O:2].[CH3:13]N(C)C=O.CI.C(=O)([O-])[O-].[K+].[K+]>O>[CH3:13][N:7]1[C:6]([C:9]([O:11][CH3:12])=[O:10])=[CH:5][C:4]([N+:1]([O-:3])=[O:2])=[N:8]1A 50-mL single-neck round-bottomed flask equipped with a magnetic stirrer was purged with nitrogen and charged with methyl 5-nitro-1H-pyrazole-3-carboxylate (156a) (0.94 g, 5.5 mmol), anhydrous N,N-dimethylformamide (11 mL), methyl iodide (0.85 g, 6 mmol) and potassium carbonate (0.83 g, 6.1 mmol). The reaction was stirred at room temperature for 16 h. After this time the reaction was diluted with water (40 mL) and extracted with methylene chloride (3×25 mL). The combined organic extracts were dried over sodium sulfate, filtered and concentrated under reduced pressure. The resulting residue was subjected to flash chromatography (silica, ethyl acetate/hexanes) to afford methyl 1-methyl-3-nitro-1H-pyrazole-5-carboxylate 156b in 66% yield (0.67 g) as a white solid: MS (ESI+) m/z 186.0 (M+H). Also isolated was the regioisomer methyl 1-methyl-5-nitro-1H-pyrazole-3-carboxylate in 15% yield (0.15 g) as a white solid: MS (ESI−) m/z 186.0 (M+H).
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